A polymer electrolyte fuel cell (PEFC) includes a membrane-electrode assembly (MEA) and a separator. At least one layer of the fuel cell forms a module and a number of modules are piled.
The MEA includes an electrolyte membrane, a first electrode (an anode) including a catalyst layer and a diffusion layer disposed on one side of the electrolyte membrane, and a second electrode (a cathode) including a catalyst layer and a diffusion layer disposed on the other side of the electrolyte membrane. In separators disposed on opposite sides of the MEA, a fuel gas passage for supplying fuel gas (e.g., hydrogen) to the anode and an oxidant gas passage for supplying oxygen gas (e.g., oxygen, usually, air) to the cathode are formed. In order to cool the fuel cell, a coolant (e.g., water) passage is formed per one fuel cell or a plurality of fuel cells in the separators. The separator constructs an electron current passage between adjacent fuel cells.
Electrical terminals, electrical insulators, and end plates are disposed at opposite ends of the pile of modules. The pile of modules are tightened between the opposite end plates in a fuel cell stacking direction and the opposite end plates are coupled to a fastening member (for example, a tension plate) extending in the fuel cell stacking direction outside the pile of fuel cells, by bolts and nuts to form a stack of fuel cells.
In the PEFC, at the anode, hydrogen is changed to positively charged hydrogen ions (i.e., protons) and electrons. The hydrogen ions move through the electrolyte membrane to the cathode where the hydrogen ions react with oxygen supplied and electrons (which are generated at an anode of the adjacent MEA and move to the cathode of the instant MEA through a separator, or which are generated at an anode of a fuel cell located at a first end of the pile of fuel cells and move to a cathode of a fuel cell located at a second, opposite end of the pile of fuel cells through an external electrical circuit) to form water as follows:At the anode: H2→2H++2e−At the cathode: 2H++2e−+(½)O2→H2O
Such a conventional PEFC is disclosed in, for example, Japanese Patent Publication 2002-50367. In the conventional PEFC, usually, the diffusion layer (gas diffusion layer) is made from at least one layer of carbon cloth or carbon paper.
However, in the conventional fuel cell, there is the following problem:
Since the diffusion layer made from layered of carbon cloths or carbon papers is low in rigidity, and the electrolyte membrane and the catalyst layer are also low in rigidity, a rib (a convex of convex and concave portions) of the gas passage of the separator intrudes on or pushes into the diffusion layer (see, e.g., region A of FIG. 6), resulting in a bending deformation of the diffusion layer and the electrolyte membrane. As a result, durability of portions of the diffusion layer and the electrolyte membrane where corners (shoulders) of the ribs of the separator contact the diffusion layer decreases, accompanied by a decrease in durability of the fuel cell.
In order to increase a rigidity of the diffusion layer thereby preventing the diffusion layer from pushing into the membrane due to pressure from the separator, it might be effective to make the diffusion layer from a wire netting or a composite carbon paper (a composite of carbon and phenol resin.
However, with the wire netting, there are problems of corrosion of the wire netting, degradation of the membrane due to the corrosion of the wire netting, and an increase in a manufacturing cost. Further, with the composite carbon paper, there is a problem that a portion of the diffusion layer compressed by the rib of the separator is collapsed and gas cannot flow through the collapsed portion of the diffusion layer.